1. Field of the Invention
The present invention relates to a method of manufacturing a plurality of light emitting devices by dividing a light emitting device wafer having a sapphire substrate layer and a light emitting layer.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby partition a plurality of regions where devices having electronic circuits such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the division lines to thereby divide the regions where the devices are formed from each other, thus obtaining the individual devices as a plurality of semiconductor chips. Further, a light emitting device wafer is provided by forming a plurality of light emitting devices such as light emitting diodes (LEDs) on the front side of a sapphire substrate. The light emitting device wafer is also cut along the division lines to obtain the individual light emitting devices such as light emitting diodes divided from each other, which are widely used in electronic/electric equipment (see Japanese Patent Laid-open No. Hei 10-56203, for example).
Cutting of such a wafer along the division lines is usually performed by using a cutting apparatus called a dicing saw. This cutting apparatus includes a chuck table for holding a workpiece such as a wafer, cutting means for cutting the workpiece held on the chuck table, and feeding means for relatively moving the chuck table and the cutting means. The cutting means includes a cutting tool having a spindle and a cutting blade mounted on the spindle, and a spindle unit having a driving mechanism for rotationally driving the spindle. In such a cutting apparatus, the cutting tool and the workpiece held on the chuck table are relatively moved and at the same time the cutting tool rotating at a speed of 20000 to 40000 rpm (revolutions per minute) is fed into the workpiece to thereby cut the workpiece.
As a method of dividing a light emitting device wafer composed of a sapphire substrate and a plurality of light emitting devices such as nitride semiconductors formed on the sapphire substrate, there has recently been proposed a method including the steps of applying a pulsed laser beam along the division lines formed on the wafer to thereby form a laser processed groove along each division line and next applying an external force to each laser processed groove to thereby break the wafer along each division line (see Japanese Patent Laid-open No. Hei 10-305420, for example). As another method of dividing this kind of wafer by laser processing, there has also been proposed a method including the steps of applying a pulsed laser beam having a transmission wavelength to the substrate of the wafer along the division lines in the condition where the focal point of the pulsed laser beam is set inside the substrate, thereby continuously forming a modified layer inside the substrate along each division line and next applying an external force to the substrate along a laser processed locus where the strength of the substrate is reduced by the formation of each modified layer, thereby breaking the wafer along each division line (see Japanese Patent No. 3408805, for example).